In general, the surface of a substrate (or a wafer) is processed using plasma for a desired purpose. For example, in order to fabricate light emitting diodes (LEDs) using a sapphire wafer to increase brightness of light, a surface of the sapphire wafer is etched in embossed patterns having a hemispherical lens shape, so that the brightness of the emitted light is increased. In this manner, in order to from the embossed patterns on the wafer surface, the wafer is covered with photoresist, is developed using a mask, and is etched by plasma etching.
In this plasma process, a wafer chucking apparatus for fixing and holding the wafer processed by the plasma in a processing chamber is required. This wafer chucking apparatus is called a tray or a wafer loader.
This conventional wafer chucking apparatus is disclosed in Korean Patent No. 10-0707996, which was granted to the applicant of the present invention.
The conventional wafer chucking apparatus includes a lower plate, on which a plurality of wafers is loaded, and an upper plate, which is coupled to an upper portion of the lower plate by a physical, mechanical tool such as a bolt and fixes the plurality of wafers loaded on the lower plate.
The lower plate of the conventional wafer chucking apparatus is formed so as to be able to load several pieces of wafers at a time, and stably transmits heat, which is generated from the wafer chucking apparatus by the plasma when the wafers are etched, to a plasma etching cathode (not shown).
However, in this conventional wafer chucking apparatus, the upper plate fixing the plurality of wafers loaded on the lower plate is made of ceramic or metal. Thus, due to properties of the material of the upper plate and a shape of the upper plate pressing the wafers, particularly a wide contact area with the wafers, etching uniformity is influenced by the heat, which is generated from the wafer chucking apparatus by the plasma when the wafers are etched, and a plasma field, so that hemispherical lens patterns are distorted at an edge zone of each wafer, and lean to one side.